Radio receiving system



G. L. BEERS RADIO RECEIVING SYSTEM Filed April 28, 1934 Sept Patented Sept. 28, 1937 UNITED STATES PATENT OFFICE RADIO RECEIVING SYSTEM George L. Beers, Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 28, 1934, Serial No. 722,877

4 Claims. (C1. Z50-20) The present invention relates to radio receivenough to produce an appreciable effect upon the ing and amplifying systems, and more particudelity characteristic of the receiving system. An larly to remote volume contro-1 means for such electric motor control system with only the moto-r systems. circuits extended to operate the compensated 5 I In providing remote control means for radio volume control system, while practical, is at the n receiving systems, it is desirable to control the same time costly. gain or signal amplitude by suitable volume con- It is, therefore, an object of the present inventrol means within the apparatus, without extion to provide an improved remote volume contending the signal conveying circuits to the retrol system for radio receiving apparatus and the 1o mote control points. This may be provided by like which is adapted to provide tone control or 10 motor control means wherein only the motor conacoustic compensation without resorting to comtrol circuits are extended to the remote control plcated Circuits iIlVOlVing SS Of fidelity 01 mOOI points. Also, in the event that the volume concontrol means. trol means for a radio receiving system is ap- It is a further object of the present invention l5 plied to high frequency circuits, the high freto provide an improved tone compensated rey15 quency amplifier tubes may be controlled directly mo-te control system for radio receiving apparaby varying the biasing potentials thereon through tus and the like, which involves simple control extension of the biasing potential circuits, withcircuits adapted to be extended to any length to out extending the signal conveying circuits. remote control points without extending the sig- However, with the advent of compensated Volnal conveying circuits. 20 ume control systems, wherein the control of'vol- It is also an object of the invention to provide ume is acoustically compensated at various sound a ltone or acoustically compensated volume conlevels, remote volume control systems heretofore trol system for radio receiving apparatus and the 5 employed are found to be not practical either belike which is adapted for remote control operacause of complicated circuits, or because of cost, tion. 25

the latter disadvantage being particularly char- In accordance with the invention, a gain conacteristic of remote motor control circuits for trol circuit including a gain controlling tube or radio apparatus. electric discharge device and a tone control net- A form of acoustically compensated volume work including a second control tube or electric control circuit is shown and described in the patdischarge device are provided with a common-grid -30 ent to Stevenson 1,788,035 for Volume control bias control circuit which may be extended to a circuits. Insuch systems, as the audio frequency remote control point in connection with a bias signal amplitude is reduced by suitable means potential control device such as a potentiometer such as a volume control potentiometer in the resistor. By this means, both ycontrol tubes are audio frequency circuit, the audio frequency controlled simultaneously, whereby, as the vol- 35 transmission characteristic is altered whereby urne or signal amplitude is reduced, the desired signals in certain frequency ranges are more tone compensation is provided. highly attenuated, thereby to compensate for the In a practical embodimentof the invention, the effect upon the ear of sounds at lower volume automatic volume control tube rof a radio re- 40 levels. For acoustical compensation of volume ceiving system is arranged to be controlled simul- 40 control means, it is necessary that the signal amtaneously with a tube having its anode circuit plitude be maintained at a predetermined level Connected With a 150116 COmDeIlSatng network in before compensation is applied for the reason the audio frequency portion of the receiving systhat definite compensation may not otherwise be tem. The biasing potential on both tubes is then provided for each sound level. This normally re- Varied simultaneously through a common exten- 45 quires a substantially at automatic volume sible control circuit thereby Veliminating the vuse control means preceding the compensated volume of motors and motor control circuits and ,the excontrol circuit as a part of the system. tension of signal conveying circuits.

Ordinarily, to provide the type of acoustically The invention will, however, be better under- .compensated volume control above referred to at stood from the following description when con- `50 Va remote point without resorting to motor conksidered in connection with the accompanying trol, necessitates operating certain conductors in drawing and its scope will be pointed `out in the a remote control cable at high audio frequency appended claims. potentials with respect to ground. 'Ihe capacity In the drawing, the ligure is a circuit diagram between conductors in such a cable may be great of a portion of a radio receiving system'provided '155 with an acoustically compensated remote volume control system embodying the invention.

Referring tothe drawing, the signal conveying circuit of a radio receiving system is represented by way of example by an electric discharge device or detector tube 5 which receives signals through an input coupling transformer 6, and which in turn is coupled through audio frequency coupling means, hereinafter described as an audio frequency electric discharge amplifier device or tube 1.

In the present example, the detector device 5 may be considered as the second detector of a superheterodyne receiving system and is provided with a cathode 8, a control grid 9, and an anode I8. The control grid 9 is connected with a tuned input circuit I I comprising the secondary I2 of the transformer 6 and a suitable tuning condenser I3, whereby it is tuned to a predetermined intermediate frequency. The primary winding I4 of the transformer is connected with the output circuit I5 of an intermediate frequency amplifier (not shown). l A Volume control electric discharge device or tube IG as an automatic volume control means is provided with a controlgrid I1 connected with the signal input circuit through a coupling condenser 33 and a grid leak resistor I8. The tube is further provided with a cathode I9 connected with the cathode 8 through a lead 23, and an output anode 2I in circuit with which is provided an anode impedance or resistor 22. Automatic volume control potentials for the preceding amplifier (not shown) is taken through an automatic volume control lead 23 from the impedance 22.

Automatic volume control systems of this character are well known and understood and, accordingly, further description is not believed to be necessary. The tube or electric discharge device I, however, represents any suitable electric discharge control means for controlling the signal amplitude of the receiving system. For purposes of the invention, the usual automatic volume control tube is well suited for this purpose. The detector device 5 is coupled to the amplifier device 'I through an audio frequency choke coil 24 in the output anode circuit 25 and a coupling condenser 26, to the input electrode or control grid 21 of the 'amplifier tube 1. The latter is provided with a cathode 28 having a self-bias resistor 29 in circuit therewith to the negative endof which the control electrode or grid 21 is connected through a suitable 'grid bias supply resistor 30. The output anode for the device 1 is indicated at 3l and may be connected to any suitable apparatus (not shown) for further vamplifying or utilizing the audio frequency signals.

The audio frequency signal conveying circuit may be represented by leads indicated at 32 and 2D between the detector device and the audio frequency amplifier device 1. Across this circuit is connected a tone control network which is to be utilized for acoustic compensation for the output signals currents of the system. Any suitable point, however, in an audio frequency system or signal receiving system may be chosen for the ap- Y plication of tone controlling means for acoustic compensation. It is preferably connected, however, across a portion of the audio frequency circuit.

By way of example, the tone control network comprises an inductance 35, a condenser 376, and a relatively high impedance element such as a Vresistor 31, in-series. The impedance element 31 Ais connected in parallel with the anode impedance of an electric discharge control device or tube 38 the anode of which is indicated at 39 and the cathode of which is indicated at 40. The cathode is connected with the cathodes 8 and I9 through the lead 2|). The impedance device 31 is a resistor, in the present example, providing a plate load impedance for the device 38 and is suiiiciently high in resistance value and the internal impedance of the device 38 is also sufliciently high to prevent the tone controlling network from normally being effective across the circuit.

The condenser 36 and choke coil or inductance 35 provide a series resonant circuit tuned to a predetermined frequency range preferably between LOOO and 1,500 cycles, or any desired frequency range in the audio frequency band about which tone compensation is desired as the signal volume is varied. The effect of the tone control network is varied by means of the device 38 the control grid of which is connected to a control or grid bias supply lead 42 with the control grid I1 of the automatic volume control tube I6. The control lead 42 is variably connected to a source of biasing potential through the movable contact 43 of a potentiometer device 44 across which is maintained a difference of potential having a polarity as indicated. A current limiting resistor 42a is included in the lead 42.

In the present example, the potentiometer resistor 44 is included in circuit at the negative end of a voltage divider resistor having two sections 45 and 45 in series across supply potential terminals indicated at 41. The anode circuits of the device 5, I6 and 38 are connected as indicated to tap points 48 on the voltage divider resistor, certain of the tap points as indicated, being preferably variable for adjustment of the potential values for proper operation of the automatic volume control tube I6 and the tone control tube 38.

With the arrangement shown, it will be seen that as the contact 43 of the potentiometer 44 is moved, the portion of the resistor 44 included between the cathode I9 and the control grid I1 of the volume control tube I6 and also between the cathode 40 and the control grid 4I of the tone control tube 38 will be Varied, thereby simultaneously varying the biasing potential applied to the said control tubes.

The circuit connections are such that the Variation of biasing potential causes the automatic volume control tube to increase the negative biasing potential applied to the automatic volume control circuit 23, and thereby reduce the signal amplitude or output volume of the system, while at the same time, the plate to cathode impedance l of the tone control device 38 is decreased as the grid 4I becomes more positive. In this manner the tone control network becomes more effective across the audio frequency channel 32-20 to reduce the audio frequency amplitude within the range of the series resonant circuit. Therefore there is provide a reduction in the signal amplitude or volume and automatically a correspondling predetermined acoustic compensation.

It will be seen that the potentiometer device I 43-44 may be of the simple resistance type having a single movable contact, and that it may be connected in circuit by merely extending the control or bias supply lead 42 and circuit connection leads indicated at 50 to any suitable point remote from the remainder of the receiving apparatus. Y

It will further be seen that since the bias con- Atrol circuit conveys only direct current or direct biasing potentials, no signal currents are con- Veyed externally of the apparatus by this system.

The detector device may be of any suitable type. In the present example, it is of the anode bend type and, accordingly, the grid 9 is connected through the secondary I2 and a supply lead 49 with a point more negative than the cathode 8 such as the negative potential supply terminal 4l', whereby the potential drop through the volume control potentiometer 44 may, at the same time, be utilized to supply the bias potential to the detector device 5 thereby eliminating the use of other potential drop producing means for that purpose.

It will be seen that the control tube 38 functions to reduce the gain of the audio frequency system within a predetermined range such as a mid-range, in the present example, and is controlled by the manual volume control means for the system which operates to adjust the bias potential applied to the volume control tube I6, which is also the automatic volume control tube of the system. The bias potential of the tone control tube is controlled simultaneously with and by the same means as the volume control tube, whereby in operation the user of the apparatus in which the system is provided obtains proper acoustic compensation by merely adjusting the volume as in the case of apparatus not having the advantage of remote control.

I claim as my invention:

1. Acoustically compensated volume control means for remote control radio receiving systems and the like, comprising a tone control network, an electric discharge tone control tube having an anode circuit connected therein and having a control grid, a volume control circuit, an electric discharge control tube in said volume control circuit, said tube having a control grid for receiving signals and an output circuit providing a gain controlling biasing potential, a control circuit connected with said grids through which circuit biasing potentials may be supplied to said grids simultaneously, and means in said circuit for simultaneously varying said biasing potentials.

2. Means for remotely controlling the volume in a signal transmission circuit with acoustic compensation, including in combination, a remote variable resistance device, a direct current bias control circuit including said device as a bias potential controlling element therein, and volume and tone control electric discharge tubes for said signal transmission circuit connected with said control circuit to receive variable biasing potentials therefrom.

3. In a radio receiver, the combination with means for receiving, detecting and amplifying a signal modulated carrier wave, of means for altering the tone of the reproduced signal, means providing automatic volume control potentials for said receiver, each of said means including an electric discharge control tube having a control grid, a cathode and an anode, a common grid bias control circuit for said tubes, and means in said circuit for simultaneously varying the grid bias applied to said tubes through said circuit.

4. In a radio receiver, the combination with means for receiving, detecting and amplifying a signal modulated carrier wave, of means for altering the tone of the reproduced signal, means providing automatic volume control potentials for said receiver, each of said means including an electric discharge control tube having a control grid, a cathode and an anode, a common grid bias control circuit for said tubes, means in said circuit for simultaneously Varying the grid bias applied to said tubes through said circuit, and means connected in series with the tone altering means for varying the eiect of said tone altering means upon the reproduced signal.

GEORGE L. BEERS. 

